Effect of preloading in high-strength bolts on bolted-connections exposed to fire

Preloading is an important process for bolted connections. Previous studies over the last few decades investigated the fire behaviour of typical bolted connections. However, there is a paucity of studies that examine the effects of preloading in high-strength bolts with respect to the responses of bolted connections that are exposed to fire. This study includes a series of numerical analyses to investigate the fire behaviour of two types of bolted connections, namely extended endplate connections and fin plate connections with and without preloading. Various parameters including preloading and thickness of the connecting plate were considered. The study also demonstrates numerical methodology with respect to preloading and parameters of the damage index by using an explicit dynamic solver. The failure modes, mid-span deflections, displacements of beam ends, and fire-induced axial forces in beams are also discussed in detail. The results indicate that preloading in the bolts has little or no effect on the response of endplate connections exposed to fire because the preloading in endplate connections is offset at the thermal expansion stage. In contrast, the fire behaviour of the fin plate connections is influenced by preloading and fin plate thickness. The use of a thinner fin plate results in the connections receiving a limited effect from the preloading in the connections in fire. The use of a stronger connecting plate in fin plate connections indicates that it is not possible to ignore the effect of preloading on the fire response of connections, and this can improve safety.